This invention relates to a control method for valve-timing changeover for internal combustion engines that have selectable modes of valve-timing operation and is primarily applied to a vehicular engine.
There has been known heretofore from the Japanese Examined Patent Application Publication No. Tokkosho 49-33289 an engine in which a valve timing for at least each one of the intake valves or the exhaust valves can be changed over as desired between a low-speed valve timing suitable for a low-speed revolution range of the engine and a high-speed valve timing suitable for a high-speed revolution range of the engine. In this type of engine, the valve timing is changed over to the low-speed valve-timing in the region or range where revolution speed of the engine is lower than a predetermined speed and the intake negative pressure of the engine is also lower than a predetermined pressure level (closer to vacuum) while it is changed over to the high-speed valve-timing in conditions other than the foregoing region.
With the foregoing arrangement of the prior art, there is a problem of changeover shocks that result from a drastic change in the engine output that occurs with changeover of the valve timing.
It is, therefore, the object of the present invention to provide a control method for valve-timing changeover in a vehicular engine such that it can minimize said changeover shocks.